How individuals who use two languages organize their phonetic system(s) has been of long-standing interest in the area of bilingual and second language (L2) speech research. Great attention has been paid to adult L2 learners, but few studies have characterized how phonetic categories emerge and develop in early acquisition and what kind of mechanisms are at play in this process in bilingual children. The main goal of this proposed study is to examine vowel and consonant production in Korean-English bilingual children in order to determine developmental patterns of speech production. In our preliminary studies, we have acoustically examined speech production in 5- and 10-year-old Korean-English bilingual children and found developmental differences between the two age groups. First, 5-year-old children established distinctive systems for each language for vowels but not for stop consonants, while 10-year-old children obtained distinctive systems for both vowels and consonants;second, both groups of children employed different underlying mechanisms. Based on these observations, we propose to further investigate speech production at two different chronological ages in order to determine more precise developmental patterns: 3- and 7-year-old children. Examination of bilingual children's speech will make significant contributions to the current literature of bilingualism in that the proposed study will allow us to explain the developmental processes by which bilingual speakers reach the level of fully established speech production. Furthermore, examining normally developing bilingual children will provide important educational and clinical implications for bilingual children with speech sound disorders. Without a clear understanding of the speech patterns in typically developing children learning two languages, it is difficult to implement speech assessment and intervention programs to serve linguistically diverse children with speech sound disorders. Thus, the results of this proposed study will provide significant information for developing speech assessment and intervention programs for bilingual children with speech sound disorders. PUBLIC HEALTH RELEVANCE: Examining speech production characteristics of normally developing bilingual children will provide important educational and clinical implications for bilingual children with speech sound disorders because the developmental speech patterns of normally developing children are commonly considered to be a diagnostic tool for speech disorders. Without a clear understanding of the speech patterns in typically developing children learning two languages, it is difficult to implement assessment and intervention programs to serve bilingual children with speech sound disorders. Thus, the results of this proposed study will provide significant information for developing speech assessment and intervention programs for bilingual children with speech sound disorders.